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NextAir18

The field of loudspeaker building was born almost a century ago, with the invention of the dynamic sound converter by Western Electric engineers Vente and Turas, and it has not seen many significant developments since then. Of course the chassis elements have been more specifically tailored for their transmission tasks, basses had more mass than mid-range speakers, and tweeters needed a much lighter membrane – but that was about it for the great advancements that resourceful marketing experts and wordy journalists like to praise with every available superlative. All right, the standard paper cone for the upper range also turned into the more technically useful textile calotte, whose membrane was then made from a variety of different materials, but the model with the 25-mm diameter has been state of the art since the mid-1960s at this point.﻿.

It is only recently that the 50-year-long dominance of the calotte has been seriously called into question – Airmotion transformers are now hammering at the gates of the wooden boxes and loudly shouting, “Let us in!” Based on a patent by Oscar Heil, the nearly weightless membrane, with its vacuum-metalized circuit path and magnetostatic drive, guarantees better resolution for even the smallest residual signals, for instance from a cymbal strike as it fades out in the room. But of course even the initial strike greatly benefits from the fact that it doesn’t have to overcome the laws of gravity first. We have a couple of these giants of sound in our arsenal too – we recently introduced the Gradient AT-1 here. In the Next Air 18, it gets the chance to prove it has just the right genes for the Blues Class.﻿.

Now, of course it can’t handle all the frequencies by itself, from down in the basement up to the attic – it needs at least one teammate that can keep up with it. Following our motto of looking for partners wherever you happen to be at the moment, we first took a look at the extensive Gradient range. The Select series was easy to ignore; the AXT series was more interesting, but it has already been combined with a couple of other tweeters and is fine the way it is. The AXPs also have a suitable magnetostat on board, so we don’t really need to change anything there. But our principles say we can do it, so let’s keep looking elsewhere. What do the playmates need to be able to do to keep up with a very light-footed AMT? Well, they need outstanding dynamics, for instance the familiar characteristics of an Eton or a Satory. Combining the pieces from Neu-Ulm, and the proven ER4 and 26 HD 1, with another peak converter would be like carrying coals to Newcastle, and we want to keep the Satories as a separate entity. When it came down to it, we didn’t grasp at straws – we just haven’t used the Excel enough in the past. Sure, they can build great tweeters in Norway, but we can imagine an AMT being a very good alternative. There is also a complete series with Nextel of coated paper membranes, ranging from the #12 to the #25 size, that lets us realize all of our ideas. For our first project, we wanted to start off slowly – the goal we set for ourselves was a classic two-way with a #17 and the AT-1. Coincidentally, the convenient W 18 NX 001 we had chosen is an old friend, one we had already used in the Nextel 18. At just under 18 liters and with a reflex balance at 44 Hz, we were going to separate the little playing chamber from our living room with a wooden case﻿.

Once the technology specifics were set, it was time to think about the cabinet. It is helpful to do a drawing before you go shopping for the boards. We use SketchUp, the free 3D drawing program from Trimble, although as commercial users we pay a reasonable licensing fee every year﻿.

There’s actually nothing too interesting about designing a wooden case to enclose 18 liters. So we made things a little more complicated for ourselves, because we wanted to avoid visible raw edges. There was an old Beckum-Elektra PK 200 sliding table saw in the basement, and I had gone back and made its extension arms wider and wider over the years. Now I can use it to cut wonderful miters on boards up to 120 cm high, so this little pile of boards was no challenge at all. For practical reasons, I only countersank the floor, and the reinforcements sit in grooves that I took out of the inside using the CNC router. That gives the structure the necessary stability and right angles when you lash it together with tension belts. The following pictures speak for themselves – no commentary needed. Click on them with the mouse to see a larger view﻿.

There’s actually nothing too interesting about designing a wooden case to enclose 18 liters. So we made things a little more complicated for ourselves, because we wanted to avoid visible raw edges. There was an old Beckum-Elektra PK 200 sliding table saw in the basement, and I had gone back and made its extension arms wider and wider over the years. Now I can use it to cut wonderful miters on boards up to 120 cm high, so this little pile of boards was no challenge at all. For practical reasons, I only countersank the floor, and the reinforcements sit in grooves that I took out of the inside using the CNC router. That gives the structure the necessary stability and right angles when you lash it together with tension belts. The following pictures speak for themselves – no commentary needed. Click on them with the mouse to see a larger view﻿.

It was no problem at all reducing the Gradient AT-1 to the right frequency measurement. All it took was a 12 dB filter and a series resistor to adjust the volume. The Excel-BMT was a bit more challenging, since its frequency curve shows two plateaus at different heights. The top one was easy to tame with a 2nd-order filter, but there was still a hump left over that made the mid-range about 3 dB too loud. Help came in the form of a broadband suction circuit, whose effects can be leveled out with a corresponding resistor. A bigger Mox leaves the range from 600 to 3000 Hz louder, and a smaller one makes it quieter. People building this loudspeaker can use an adjustment screw to move the stage forward or back according to their own taste. The Branch_Total Curve shows a perfectly executed coupling of the two chassis elements when they are soldered on in phase opposition. Naturally, we also corrected the impedance, as a precaution for tube fans.

There are a couple of special features to pay attention to in the last couple of steps for the new loudspeaker, so we took two or three more pictures.

For the crossover, we mounted the coils far enough apart to make sure they don’t change each others’ values. The tweeter doesn’t like to be blasted from the back by the bass, so we glued a 12 x 12 cm board behind its cutout. In order to give it some play when we soldered it on, while still keeping the wires out of the way, we fed them through two drilled holes. Of course we closed them up again afterward, otherwise it would whistle.
There are two bags of Sonofil in the box – two mats behind the tweeter chamber and one on either side of the bass, on the right and left. The opening for the reflex channel stays clear. For the tweeter, the wide flag is the positive pole, and for the bass it is marked in red. Don’t forget to pre-drill holes before screwing in the chassis elements!

All that’s left now are the measurement diagrams:

Frequency responce

Impedance

Frequency under 0/ 30/ 60°﻿﻿

Distortion at 90 dB﻿

Step responce

Waterfall

﻿
... and now I’m sure there are a few people who have caught the bug and are sitting on the edge of their seats in front of the monitor, because it’s time for the sound description. Will he draw comparisons, make rankings, or maybe even give me some decision-making tips so I don’t have to do my own listening session? None of the above, because we had to rely on our own ears, which are no more definitive than anyone else’s. All too often, people forget that listening takes place in the brain, where external changes in pressure flow together to create an occurrence that we describe as sound. We often find that we perceive music differently during a listening test than our visitors do – and yet it is impossible to say that someone experienced the wrong thing. Different aspects were important to us in each case, and everyone was right. "Wow, what a great bass," says one person. "Where?" asks the other. If there were only one correct opinion about how music should be represented, we would need at most four different sizes of speakers to account for every taste in every room. But since no sound converter will ever be able to represent instruments and voices in a perfectly natural way, we have to live with compromises that affect everyone differently. How some people feel entitled to force their narrow auditory worldview onto others, we will never understand. But enough audience critique – let’s get to the listening experience.

We connected the Next Air 18 to the tube in the listening room, which as you know has been fed not just by the record player, but also by the computer for a while now. We fired up the tablet and – no, this time we didn’t play the usual musical program. This time we let Media Monkey’s random generator pick the tracks, which meant we didn’t just get to hear recordings for audiophiles. In the jazz department, we were lucky enough to hear Dave Brubeck’s “Take Five” from the legendary album “We’re all together again for the first time” first, which made us warm up to the Next Air right away. Everything fit well – the alto and baritone saxes had their typical character, the piano strikes were precise, the bass steadily plucked its four notes, each musician had a place on the stage, and when Alan Dawson pounded out the (admittedly simple) melody on his bass drum, accompanied by manic drum rolls and rattling cymbals, the audience in Berlin – almost 43 years ago to the day – were not the only ones who got excited. The demonstration continued with an amazingly bass-heavy – well, modern – mix for the little box, with Club de Beluga’s “It’s a beautiful day.” Tom Rotella followed with “The Immigrant” and his sensitive guitar; the strumming and picking sounds were clear but not in the foreground, and the room was filled with music all the way around the back of the boxes. The classical selection started off with Schumann’s “Träumerei,” a big grand piano in a concert hall, the echo of the walls and a long vibration of the strings. Large orchestras had every instrument from kettledrum to triangle accounted for, and the voices were plausible, whether it was a bass baritone or a soprano. Once we had found no faults with rock or blues, either – I don’t know whether I’ve ever listened to “Killing in the Name” by “Rage Against the Machine” and tapped my foot all the way to the end like that before – we wrapped up our brief test, concluding that we had made the right equipment choice for the Next Air 18. How it performs compared to the Eton, Satory or Gradient Audible? That’s something people have to decide for themselves, after listening to it with their own ears and based on their personal taste﻿.